Predictive prey pursuit in a whiskered robot

Highly active small mammals need to capture prey rapidly and with a high success rate if they are to survive. We consider the case of the Etruscan shrew, which hunts prey including crickets almost as large as itself, and relies on its whiskers (vibrissae) to complete a kill. We model this hunting behaviour using a whiskered robot. Shrews strike rapidly and accurately after gathering very limited sensory information; we attempt to match this performance by using model-based simultaneous discrimination and localisation of a ‘prey’ robot (i.e. by using strong priors). We report performance that is comparable, given the spatial and temporal scale differences, to shrew performance in most respects

The neurobiology of Etruscan shrew active touch

The Etruscan shrew, Suncus etruscus, is not only the smallest terrestrial mammal, but also one of the fastest and most tactile hunters described to date. The shrew's skeletal muscle consists entirely of fast-twitch types and lacks slow fibres. Etruscan shrews detect, overwhelm, and kill insect prey in large numbers in darkness. The cricket prey is exquisitely mechanosensitive and fast-moving, and is as big as the shrew itself. Experiments with prey replica show that shape cues are both necessary and sufficient for evoking attacks. Shrew attacks are whisker guided by motion- and size-invariant Gestalt-like prey representations. Shrews often attack their prey prior to any signs of evasive manoeuvres. Shrews whisk at frequencies of approximately 14 Hz and can react with latencies as short as 25–30 ms to prey movement. The speed of attacks suggests that shrews identify and classify prey with a single touch. Large parts of the shrew's brain respond to vibrissal touch, which is represented in at least four cortical areas comprising collectively about a third of the cortical volume. Etruscan shrews can enter a torpid state and reduce their body temperature; we observed that cortical response latencies become two to three times longer when body temperature drops from 36°C to 24°C, suggesting that endothermy contributes to the animal's high-speed sensorimotor performance. We argue that small size, high-speed behaviour and extreme dependence on touch are not coincidental, but reflect an evolutionary strategy, in which the metabolic costs of small body size are outweighed by the advantages of being a short-range high-speed touch and kill predator

Analysis of calcium signals evoked by sensory stimuli in different layers of somatosensory cortex of the Etruscan shrew

The Etruscan shrew, Suncus etruscus, is the smallest terrestrial mammal with a body weight of ~ 2 g and a body length of ~ 4 cm. The small size of the Etruscan shrew’s brain offers particular advantages for imaging, as the entire cortical sheet as well as somatosensory cortex are on average less than 500 µm thick. Here we show that in this animal two photon imaging allows to visualize all cortical layers, which is typically difficult to do in rodents or other mammals. Although much is known about the activity of individual cells, the pattern of activity across an entire column during sensory stimulation is less well understood. Using bulk loading of calcium indicators in the somatosensory cortex of anaesthetized shrews, we aim to describe the cellular activity of populations of neurons in somatosensory cortex across different layers. We characterize single-neuron and multi-neuron responses to whisker stimuli using optically recorded calcium transients. Our preliminary data indicate that responses are heterogeneous in Etruscan shrew cortex. Much like observed previously in rodent somatosensory cortex there is little spontaneous activity and even powerful stimuli (air puffs) evoke only sparse responses

Translaminar imaging of calcium signals evoked by sensory stimuli in Etruscan shrew somatosensory cortex

The Etruscan shrew, Suncus etruscus, is the smallest terrestrial mammal with a body weight of ~ 2 g and a body length of ~ 4 cm. The small size of the Etruscan shrew’s brain offers particular advantages for imaging, as the entire cortical sheet as well as somatosensory cortex are on average less than 500 µm thick. Here we show that in this animal two photon imaging allows to visualize all cortical layers, which is typically difficult to do in rodents or other mammals. Although much is known about the activity of individual cells, the pattern of activity across an entire column during sensory stimulation is less well understood. Using bulk loading of calcium indicators in the somatosensory cortex of anaesthetized shrews, we aim to describe the cellular activity of populations of neurons in somatosensory cortex across different layers. We characterize single-neuron and multi-neuron responses to whisker stimuli using optically recorded calcium transients. Our preliminary data indicate that responses are heterogeneous in Etruscan shrew cortex. Much like observed previously in rodent somatosensory cortex there is little spontaneous activity and even powerful stimuli (air puffs) evoke only sparse responses

Activity-dependent clustering of functional synaptic inputs on developing hippocampal dendrites.

During brain development, before sensory systems become functional, neuronal networks spontaneously generate repetitive bursts of neuronal activity, which are typically synchronized across many neurons. Such activity patterns have been described on the level of networks and cells, but the fine-structure of inputs received by an individual neuron during spontaneous network activity has not been studied. Here, we used calcium imaging to record activity at many synapses of hippocampal pyramidal neurons simultaneously to establish the activity patterns in the majority of synapses of an entire cell. Analysis of the spatiotemporal patterns of synaptic activity revealed a fine-scale connectivity rule: neighboring synapses (<16 mu m intersynapse distance) are more likely to be coactive than synapses that are farther away from each other. Blocking spiking activity or NMDA receptor activation revealed that the clustering of synaptic inputs required neuronal activity, demonstrating a role of developmentally expressed spontaneous activity for connecting neurons with subcellular precision

Homeostatic shutdown of long-term potentiation in the adult hippocampus

Homeostasis is a key concept in biology. It enables ecosystems, organisms, organs, and cells to adjust their operating range to values that ensure optimal performance. Homeostatic regulation of the strength of neuronal connections has been shown to play an important role in the development of the nervous system. Here we investigate whether mature neurons also possess mechanisms to prevent the strengthening of input synapses once the limit of their operating range has been reached. Using electrophysiological recordings in hippocampal slices, we show that such a mechanism exists but comes into play only after a considerable number of synapses have been potentiated. Thus, adult neurons can sustain a substantial amount of synaptic strengthening but, once a certain threshold of potentiation is exceeded, homeostatic regulation ensures that no further strengthening can occur